Reference
Reference
Short, sourced entries for the things the tools act on. Each entry states the definition, the facts, the causes and the fixes, then hands you the matching tool.
Web & HTTP
HTTP Status Codes — Meanings, Causes and Fixes
What each HTTP status code means, when a server should return it, what causes it in practice and how to fix it. Facts from RFC 9110, paired with free debugging tools.
30 entries →HTTP Header Reference
What the common HTTP request and response headers mean, how they are parsed, and which ones carry security consequences. Facts from RFC 9110, RFC 9111 and RFC 6265, paired with a header inspector.
15 entries →MIME Types and Content Types — Reference
What each common media type is for, which file extensions map to it, how browsers and servers treat it, and the mistakes that break uploads and APIs.
23 entries →Networking
Encoding & data
QR Code Reference
How QR codes actually work: error correction, versions, capacity, quiet zones, mask patterns, Micro QR and the Wi-Fi QR payload format — each entry paired with a generator.
13 entries →UUID Reference
UUID versions explained with the bits that matter: v4 randomness, v7 time ordering, v1/v3/v5 construction, the nil UUID, GUID differences and collision math — each with a generator.
11 entries →Design & frontend
Color Format Reference
Hex, RGB, HSL, HSV, CMYK, alpha and WCAG contrast explained with exact ranges and formulas — each entry paired with a converter that runs in your browser.
10 entries →CSS Unit Reference
How CSS length units actually resolve: px, rem, em, ch, ex, viewport units, percentages, grid fr and calc/clamp. Facts from the CSS Values specification, paired with a px/rem converter.
10 entries →Time & scheduling
Text & patterns
Regular Expression Reference
How regular expression syntax works in JavaScript and common engines: character classes, quantifiers, anchors, groups, lookaround, backreferences, flags and backtracking. Facts from the ECMAScript and PCRE specifications, paired with a regex tester.
10 entries →Markdown Reference
Markdown syntax with the edge cases that actually bite: headings, paragraphs, emphasis, links, images, lists, code, blockquotes, tables and task lists. Facts from CommonMark and GitHub Flavored Markdown, paired with a live previewer.
10 entries →